-9up to distances of several thousand miles from surface bursts of high
fission yield megaton range weapons.
They are of lesser importance with
fallout (off-site) from kiloton range tests.
Hartgering's studies suggest
that under these circumstances the amounts are amall in absolute terms and
that the radioactivity my gain access to the human body by inhalation
rather than by going through the food chain.
From the standpoint of the
long-term world-wide fallout hasard, however, these isotopes are of little
concern.
The important fission products from the standpoint of world-wide,
or delayed fallout, are Sr-90 and Cs-137 with half-lives of 28 and 27
years, respectively.
Their importance in delayed fallout lies in their
relatively long half-lives, and their ready assimilation by the human
body and the fact that they are produced in relatively large quantities
in the fission process.
taken up by the body.
taken up by plants.
Ce~-144 of half-life 275 days is also readily
It belongs to the rare earths and is not readily
Having an intermediate half-life it might be of some
concern were it present in greater quantities than it is and more readily
absorbed from the soil by vegetation into the food chain,
Finally, a word concerning Pu-239 (22).
Although the mass of
plutonium disseminated by a nuclear detonation may be greater than the mass
of strontium90 or of cesium-137 it is taken up very poorly from the soil
by plants — only about one part in 10,000.
Further, the human intestinal
tract takes up only about one part in 10,000 to one part in 100,000 of Pu
which may be present in the food.
Adding to these facts knowledge of the
amounts actually disversed in nuclear tests one can readily dismiss Pu
as unimportant in the long-term fallout problem.